1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing a resin structure reinforced with long fibers. More particularly, the invention relates to an apparatus and a method for manufacturing a resin structure reinforced with long fibers in which an oscillation mechanism for varying the position at which a resin-impregnated continuous fiber bundle is taken up is provided, thereby preventing an uneven abrasion of an endless belt or a roll of the take-up apparatus and enabling a long-term continuous operation.
2. Background of the Invention
Resin structures reinforced with long fibers in which thermoplastic resins are reinforced with continuous fibers have become of much interest in recent years, since they have physical characteristics much superior to those reinforced with short fibers. They are generally manufactured by a so-called pultrusion method in which a continuous reinforcing fiber bundle is impregnated with a thermoplastic resin while the fiber bundle is drawn through a cross-head extruder and then pulled through a die (U.S. Pat. No. 3,993,726), or a continuous reinforcing fiber bundle is immersed in a thermoplastic resin melt to wet it while it is drawn and then pulled through a die (Japanese Patent Application Laid-open (kokai) No. 57-181852).
In the manufacture of a resin structure reinforced with long fibers, in order to have a continuous fiber bundle uniformly impregnated with a matrix resin while drawing the fiber bundle, a take-up step is required in a downstream section for taking up a resin-impregnated continuous fiber bundle. This take-up step is performed in such a manner that a resin-impregnated continuous fiber bundle is sandwiched between upper and lower endless belts which are generally driven by rolls or between a pair of rolls. Generally, the resin-impregnated continuous fiber bundle passes through a shaping die immediately after an impregnation step, during which uniform impregnation is obtained and the cross section of the fiber bundle becomes to have a shape of the target product. Accordingly, in the take-up step, the fiber bundle is required to have a certain hardness so that the shape imparted at the entrance section of the take-up step is not deformed. Moreover, from the viewpoint of easy operation, it is preferred that the fiber bundle be cooled to solidify rather than being in a soft state when a resin-impregnated continuous fiber bundle is being taken up.
A take-up apparatus transfers a resin-impregnated continuous fiber bundle by the rotation of take-up rolls while imparting the fiber bundle with tension. Usually, a resin-impregnated continuous fiber bundle is sandwiched between two take-up rolls which have endless belts passed around them and which are disposed in an upper and lower relation facing each other. The fiber bundle is securely held as it is pressurized between the two take-up rolls, and the rotation of the rolls causes the resin-impregnated continuous fiber bundle to pass through a shaping die in the direction from the upstream side of the take-up roll to the downstream side of the roll. On the other hand, the resin-impregnated continuous fiber bundle is usually solidified as described before from the viewpoint of easiness in operation, etc. In order to take up each resin-impregnated continuous fiber bundle, the endless belts must have sufficient strength and softness to some extent. To meet these requirements, the endless belts are usually made of a rubber-reinforced plastic, elastomer, thermoplastic elastomer, and a natural rubber. The use of such materials, however, tends to cause a deformation due to the pressure applied for securing the resin-impregnated continuous fiber bundle. Moreover, since friction occurs due to the pressure and tension for taking up, and since the resin-impregnated continuous fiber bundle is always carried by the same portion of each endless belt, the belt is unevenly ground by the fiber bundle to form a rut. The rut gradually becomes deeper to finally reach the situation that the endless belts can no longer apply sufficient pressure to the resin-impregnated continuous fiber bundle and therefore it becomes difficult to take up the fiber bundle. If such a situation occurs, the endless belts are planed to obtain a flat surface for the purpose of reuse, or the belts are replaced with new ones. However, planing and exchanging are cumbersome and costly. In addition, during a planing or exchanging operation, manufacture of resin-impregnated continuous fiber bundles must be stopped, causing a reduction in productivity. These problems also happen when a pair of rolls are employed as the take-up apparatus. Accordingly, it is desired to develop an apparatus for manufacturing a resin structure reinforced with long fibers equipped with a take-up apparatus in which the whole surfaces of endless belts or rolls can be utilized, thereby reducing uneven abrasion and prolonging the service life of the endless belts or rolls.
In view of the forgoing situation, the inventors of the present invention studied in detail focusing on the take-up section for a resin-impregnated continuous fiber bundle in an apparatus for manufacturing a resin structure reinforced with long fibers, and as a result, found that the aforementioned problems can be solved by varying the contact point between an endless belt or a roll and a resin-impregnated continuous fiber bundle during a take-up step. The present invention was completed based on this finding.